Use of nanoparticles as lubricity additive in well fluids

ABSTRACT

A use of nanoparticles in a well fluid for improved lubricity is disclosed herein. The nanoparticles are present in the well fluid in low amounts below 5 wt %. The nanoparticles may be formed ex situ and added to the fluid or in situ in the fluid. In one aspect, the well fluid is a drilling fluid. In a further aspect, the well fluid is an invert emulsion based fluid or an aqueous based fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of PCT/CA2012/050075filed Feb. 9, 2012, which is incorporated herein by reference in itsentirety.

FIELD

The present disclosure relates generally to well fluids withnanoparticles as lubricity additives for improving lubricity, increasedrate of penetration, and/or decreasing wellbore friction. In one aspect,the well fluid is drilling fluid used during drilling of undergroundformations.

BACKGROUND

Friction dissipates energy and causes wear resulting in damage to theequipment. The way to ensure that frictional effects are minimized isthrough proper lubrication. In carrying out this function, lubricantscreate a lubricant film on surfaces of moving parts. Lubricant additivescan be used in automobiles, lubricants, greases, metal working fluids,oil and gas drilling, heavy machinery and other related industries.

The type of drilling fluids chosen for a given drilling operationdepends on the formation being drilled, the depth, the mechanicalresistance, and the pressure of the wellbore. Regardless of their type,drilling fluids maintain hole integrity, remove cuttings from the hole,prevent formation damage, suspend cuttings and weighting materials whencirculation is stopped, cake off the permeable formation by preventingthe passage of fluid into the formation, and cool down and lubricate thedrill bit.

Even if a drilling fluid successfully meets all of the aboverequirements, there is no guarantee that the rate of penetration will beacceptable, since poor lubricity and high friction and drag increasepipe sticking and drilling cycle. The need to overcoming frictionalforces is very much encountered during all stages of wells construction;including drilling, completion and maintenance, which originates fromthe rotation and/or sliding of a pipe inside the well in contact witheither the wellbore (metal-to-rock) or the casing (metal-to-metal).These forces hinder directional and extended reach drilling by creatingexcessive torque and drag. Excessive torque and drag in highlydirectional and extended-reach wells can exceed the mechanical limits ofthe drilling equipment, which may expedite wear and tear of down holetools and equipment and thereby limit production. These problems can beminimized by using drilling fluid with high capabilities of lubricatingthe different components.

Historically, oil-based products have been used as lubricants for thedrilling operations. However, recent environmental regulations limit theusage of aromatic-based oil and require the adaptation of mineral oil,synthetic oil and water based mud where lubricant additives are founduseful to increase the lubricity (Riley et al., 2012; Kercheville et al.1986). In these instances, lubrication is achieved using additives suchas liquid lubricants, including glycols, oils, esters, fatty acidesters, surfactants and polymer-based lubricants; and solid lubricants,such as graphite, calcium carbonate flakes, glass and plastic beads(Hoskins, 2010; Skalle et al., 1999). The main function of theseadditives is to lubricate the drill string and prevent differentialsticking. But these available lubricants have not proven entirelyeffective and suffer from different disadvantages. Both liquid and largesized solid lubricants can cause permanent damage to the formation(Hoskins, 2010; Skalle et al., 1999; Lammons, 1984). Furthermore, microand macro sized solid lubricants can interfere with drilling equipmentand hinder production. The abrasive nature of macro and/or micro sizedsolid lubricants may cause higher kinetic energy and accelerate oraggravate the wear and tear of the downhole equipment (Amanullah et al.,2011). Some of these solids, nevertheless, get filtered out in thesolids control equipment due to their large size and are, therefore,less problematic. Liquid lubricants can also negatively impact thephysical and chemical properties of the drilling fluid and lead tofoaming (Hoskins, 2010). To counter foaming, costly defoamers must beadded to the system. Liquid lubricants form a film between two surfacesand, hence, minimize frequent contact and consequently friction.However, their efficiency largely depends on mud type and may depreciatein the presence of other types of mud additives. It should also be notedthat the efficiency of liquid lubricants is entirely lost in high-solidsmuds. Solid lubricants, on the other hand, do not depreciate as much insuch muds (Hoskins, 2010; Skalle et al., 1999). However, these materialsare not sufficiently effective to serve their primary goals of reducingthe coefficient of friction.

By virtue of their very small sizes, nanoparticles (NPs) have thepotential of acting as effective lubricant additives. Their size andshape enable them to enter contact zones between surfaces easily.Inorganic nanoparticles mostly do not display any affinity to oil andmay not be affected by the mud type. In-situ and ex-situ techniques forforming a wide variety of well dispersed NPs in an invert emulsion aswell as water-based drilling fluid have been detailed in the art (Huseinet al., 2012). These methods rely heavily on high shearing, whichproduces finely dispersed water pools, in the case of invert emulsiondrilling fluids, and the use of these water pools as nanoreactors toform NPs with sizes mainly below 100 nm. Once formed, these NPs displayvery high stability in the mother drilling fluid and interact veryeffectively with the rest of the drilling fluid (Husein et al., 2012).Previous experiments showed that these particles perfectly seal filtercakes by creating crack-free, very smooth surfaces (Husein et al.,2012). Therefore, these particles contribute to the formation ofslippery layers between the borehole and the drill string leading tolower overall friction coefficient and, subsequently, increase theextended reach of horizontal drilling. Moreover, due to the small sizesof these particles, the wear and tear of down hole equipment and toolsbecomes negligible as less kinetic energy (nano sized particles achievelower sedimentation speed compare to the large sized particles) andabrasive action is encountered. Overall, the application ofnanoparticles in drilling fluid presents a good potential for reducingfriction while drilling and, hence, improve the extended reach.

Nanoparticles and nano-emulsion particularly have previously been usedin drilling fluids and hydrocarbons for a variety of purposes.

U.S. Patent 20080234149 A1 (2008) is directed to a nanoparticles-basedlubricant composed of solid lubricant nano-material (material selectedfrom molybdenum disulphide, tungsten disulphide, gold, silver, lead andtin) having a size less than or equal to 500 nm and a second materialwhich is a chemical surface active agent placed on an external surfaceof the nanoparticles to minimize particles agglomeration. Thenanoparticle preparation protocol is not straight forward and involvesmany steps, which makes the approach commercially unattractive. Thispatent does not describe the use of the product particles in drillingfluids, and does not refer to the use of ferric hydroxide and calciumcarbonate nanoparticles.

U.S. Pat. No. 6,710,020 (2004) discloses the application ofhollow-inorganic fullerene (IF) nanoparticles as a lubricating additivefor automotive transport applications. IF nanoparticles having diametersbetween 10 and 200 nm are slowly released to the surface from its basemetal to provide lubrication. These nano-materials are synthesized in afluidized bed reactor at 850° C. and require different cleaning andpurification steps before they could be used. This technique ofnanoparticle preparation produces particles with high surface activity,which tends to bind the particles together and limits the quantity ofnanoparticles produced. This patent does not include measurements offriction coefficient of drilling fluids.

U.S. Patent 2011/162845 discloses a method of servicing a wellbore. Itintroduces a lost circulation composition into a lost circulation zoneto reduce the loss of fluid into the formation. The lost circulationcomposition comprises Portland cement in an amount of about 10 wt % toabout 20 wt % of the lost circulation composition, 1 to 100 nmnano-silica of 0.5 wt % to 4 wt %, 5 wt % to 10 wt % amorphous silica,0.5 wt % to 2 wt % synthetic clay, 15 wt % to 50 wt % sub-micron sizedcalcium carbonate and 60 wt % to 75 wt % water. The lost circulationcompositions rapidly developed static gel strength and remained pumpablefor at least about 1 day. The sample was observed to gel while staticbut returned to liquid upon application of shear. This patent only showsthe effectiveness in terms of lost circulation control by nano-materialsand does not provide any data on friction coefficient of the drillingfluid.

U.S. Patent Application 2009/82230 (2009) relates to an aqueous-basedwell treatment fluid, including drilling fluids, containing aviscosifying additive. The additive has calcium carbonate nanoparticleswith a median particle size of less than or equal to 1 μm. The amount ofcalcium carbonate nanoparticles used in the drilling fluid isapproximately 20 wt %. The nanoparticles used in the well treatmentfluid were capable of being suspended in the fluid without the aid of apolymeric viscosifying agent. The addition of nanoparticles altered theviscosity of the fluid. Nanoparticles suspended in a well treatmentfluid exhibited sagging (inadequate suspension properties) particularlyat high temperatures of around 350° F. The viscosity changes of a fluidupon addition of nanoparticles were well reported. However, even withthe high amount of nanoparticles added to the fluid formulation, nofluid loss and lubricity data were reported.

U.S. Pat. No. 8,071,510 (2011) is directed to a method of increasing thelubricity or reducing the coefficient of friction of a drilling orcompletion fluid by using brine of at least one water soluble salt,vegetable oil and an anionic or non-ionic surfactant in order to assistin the solubilization of the salt. This patent does not describe the useof the nanoparticles for reducing the coefficient of friction. Further,the present inventors have found that sodium salts have a negativeimpact on lubricity quality, as set out below.

Yang et al. (2012) developed a nanoscale emulsion lubricating materialto solve the high friction drag in drilling operation. It increasedlubricity by 50 wt %, but did not improve fluid loss and viscosityproperty. Their work did not involve nanoparticles.

Riley et al. (2012) studied the addition of silica-based nanoparticlesin drilling fluid and reported 20% lower coefficient of friction uponapplying 150 lb/lbs of torque.

Other references, such as Amanullah et al. 2011, consider the use ofsmall amounts of nanoparticles in water and indicate the potential forbeneficial effects on differential sticking, torque reduction andreduction of drag problems in certain types of drilling. However, thesereferences experiment with nanoparticles in water and require veryactive stabilizers to maintain the nanoparticle dispersions or look atthe interaction of nanoparticles with other components that may bepresent in a well fluid. The references do not provide data directlyrelevant to lubricity results in industrial drilling fluids but merelyindicate further areas for research.

It is, therefore, desirable to provide an improved drilling fluid havinga decreased coefficient of friction.

SUMMARY

It is an object of the present disclosure to obviate or mitigate atleast one disadvantage of previous fluids.

The present disclosure is directed to nanoparticles for use in wellfluids, and in one aspect, drilling fluids, as a lubricity additive toreduce friction and increase lubricity. The lubricity additive willreduce the co-efficient of friction at a given torque.

In one aspect, the nanoparticles are hydroxide, and/or carbonatenanoparticles. The nanoparticles are present in the fluid in lowamounts. The nanoparticles are present in amounts of less than 5 wt %,and may be present in amounts between 0.1 wt % and 4 wt %, and in afurther aspect between 1 wt % and 4 wt %. As a result, the nanoparticlesdo not significantly alter the other characteristics of the fluid.

In one aspect, the nanoparticles useful as a lubricity additive areformed ex situ and added to the well fluid or formed in situ in thefluid.

In a further aspect, the nanoparticles are formed ex situ, by providingaqueous-based precursor solutions for forming the nanoparticles, mixingthe precursor solutions under high shear, and adding the mixed productsuspension to the well fluid under high shear to form thenanoparticle-containing well fluid, wherein the nanoparticles act as alubricity additive.

In a further aspect, the nanoparticles are formed in situ, by providingaqueous-based precursor solutions for forming the nanoparticles, addingthe precursor solutions successively to the well fluid, and subjectingthe fluid to mixing and shearing to form the nanoparticles in the fluid,wherein the nanoparticles act as lubricity additive.

In another aspect, the nanoparticles are formed in situ, comprising thesteps of providing the solid precursor for forming the nanoparticles,adding the precursors successively or simultaneously to the well fluid,and subjecting the fluid to mixing and shearing to form thenanoparticles in the fluid, wherein the nanoparticles act as lubricityadditive.

Other aspects and features of the present disclosure will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific aspects in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure will now be described, by way ofexample only, with reference to the attached Figures.

FIG. 1 is a schematic diagram of the procedure used to make thenanoparticles ex situ.

FIG. 2 is a schematic diagram of the procedure used to make thenanoparticles in situ.

FIG. 3 is a schematic diagram of a further procedure used to make thenanoparticles in situ.

DETAILED DESCRIPTION

Generally, the present disclosure provides a use of nanoparticles as alubricity additive in a well fluid, and, in one aspect, in a drillingfluid. The lubricity additive reduces the friction and increaseslubricity.

The nanoparticle-containing fluids have one or more of the followingadvantages. The nanoparticles act as a lubricity additive to reduce thecoefficient of friction as compared to fluids without the nanoparticles.The nanoparticles form a thin, slippery and firm filter cake in theformation which can help reduce fluid loss that causes minimal formationdamage. They result in less torque and drag. Also, particles that areembedded in the wall cake provide a load-bearing surface between pipeand therefore increasing extended reach wells, deviated and horizontaldrilling. Nanoparticles will also pass the solids control equipmentunspoiled. They are stable at extremely high temperatures. Thenanoparticles are present in the fluids at low concentrations and may beused without other lubricant materials. The low concentration results inless formation damage, no significant change to the characteristic ofthe fluid and an increase in productivity index. The nanoparticles canbe formed ex situ and added to the fluid or formed in situ in the fluid.This results in time and cost savings.

The well fluid can be any fluid that is pumped in pipes or flows througha formation. Any such fluid needs to display low friction, otherwisepumping costs will be significant. In particular, the well fluid is akill fluid, completion fluid, pre-stimulation fluid or drilling fluid.In one aspect, it is a drilling fluid. Although this disclosuredescribes the fluid as a drilling fluid, a skilled person willunderstand that the nanoparticles may be used as a lubricity additive inany well fluid.

In one aspect, the well fluids are aqueous-based or invert emulsionfluids. Hydrocarbon based emulsions contain a large amount, i.e. 95 vol%, hydrocarbon based material (oil) as the continuous phase of theemulsion. The remainder of the emulsion is a minor amount of an aqueousphase as the discontinuous phase of the emulsion.

The well fluids, and in one aspect drilling fluids, may contain a numberof common additives such as weighting agents, emulsifiers, surfactants,foaming agents, surfactants, etc. The nanoparticles and theirconcentrations are selected such that they do not affect the othercharacteristics of the fluid.

In one aspect, the nanoparticles are selected from metal hydroxides,e.g. iron hydroxide, metal carbonates, e.g. calcium carbonate. Theseparticles may act as lost circulation material in addition to lubricityadditive.

The synthesis of the nanoparticles (NPs) additive is a chemo-mechanicalprocess. The unique process enables finely disperse NPs formation in thewater-in-oil based fluids (invert emulsion fluids) as well aswater-based fluids. As a result, the NPs can be easily inserted into thecurrent lubricant system. The severity of the drilling process,nevertheless, may induce particle agglomeration. However, thesurfactants existing in drilling fluid would act as stabilizers andwould limit agglomeration through steric hindrance. In one aspect, thenanoparticles have a particle size in the range of 1 to 120 nm and in afurther aspect the majority or most of the nanoparticles have a particlesize in the range of 1 to 30 nm. In a further aspect, substantially allof the nanoparticles have a particle size is the range of 1 to 30 nm.

Nanoparticles based lubricant additive is prepared through a proprietarymanufacturing process according to Zakaria et al. (2012) and Husein etal. (2012).

Lubricants play an important role in reducing friction and wear andpreventing component failure. Economically affordable nanoparticles arecombined with the invert emulsion well fluids or water-based well fluidsto achieve the desired lubricity property. Characterization of thenanoparticles is accomplished through powder X-ray diffraction patterns(XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM)and transmission electron microscopy (TEM). The results for drillingfluids are disclosed in PCT/CA2012/50075 (Husein et al., 2012). NPs areable to stop the intrusion of fluid into the formation as well asincrease the lubricity during drilling.

NP-based lubricants are nanosized solid particles, which are chemicallyand physically stable. Under the conditions of load and temperatureresulting from the contacting surfaces, these NPs furnish a thin film oflubricant layer on the contacting surfaces leading to reduced frictionbetween the surfaces. The lubrication effect is influenced by thehydrodynamic properties of the fluid and the size of the NPs.

The drilling fluid transports the solid lubricant NPs to the contactingsurfaces.

In a further aspect of the disclosure, the nanoparticles in the fluidcan be made using either in situ or ex situ techniques. The in situtechnique is preferred.

The NPs can be formed in situ in the well fluid. This eliminates thehandling and agglomeration problems present with many commercialprepared nanoparticles. In this method, aqueous precursors of the NPsare added to the well fluid and mixed thoroughly. High shear is appliedto the well fluid to ensure intimate mixing for the formation of stableultradispersed NPs in the well fluid. The stability of the resultant NPshinges upon particle size.

In another aspect, the in situ NPs are prepared by directly adding thesolid precursors into the well fluid coupled with intensive mixing andshearing. One needs to ensure that the volume and chemical compositionof the innate water in the well fluid allows for complete dissolution ofthe precursors.

In the ex situ process, the NPs are pre-prepared from their precursors.Precursors, in one aspect aqueous precursor solutions, are mixed underhigh shearing. The resultant NPs are then added to the well fluid underhigh mixing and shearing.

The mixing and shearing needed for NPs formation may easily be madeavailable on an oil rig. Special in-line mixers or shearing availablefrom the high pressure pump should provide the needed mixing.Experimental results showed that 1 wt % of Fe(OH)₃ or 4 wt % of CaCO₃NPs induce appreciable reduction in the coefficient of friction.Moreover, at the level of NPs added, no impact on drilling fluidspecific gravity, apparent viscosity and pH was observed.

1. DRILLING FLUID SAMPLES

The invert emulsion was supplied by a Calgary based drilling fluidcompany. One mix of the drilling fluid namely, 90 oil: 10 water (V/V)was tested. The composition of the invert emulsion drilling fluid isshown in Table 1.

TABLE 1 Compositions of drilling fluid samples Oil:water (V/V) = 90:10Base Oil = Low-aromatic hydrotreated oil Brine = 30% Calcium ChlorideOrganophillic Clays = 15 kg/m3 Hot Lime = 35 kg/m3 Primary Emulsifier =10 L/m3 Secondary Emulsifier = 5 L/m3

The NP concentration was maintained at 1 wt % and 4 wt % for the in situand ex situ prepared Fe(OH)₃ and CaCO₃ particles, respectively.

2. PREPARATION OF IRON (III) HYDROXIDE AND CALCIUM CARBONATE NPS AND THENP-BASED DRILLING FLUID IRON (III) HYDROXIDE NPS

Iron (III) hydroxide NPs were prepared by aqueous reaction between FeCl₃and NaOH at specified temperature and rate of mixing as per thefollowing reaction.

FeCl_(3(aq))+3NaOH_((aq)→)Fe(OH)_(3(s))+3NaCl_((aq))   (R1)

Ex situ preparation: Iron hydroxide NPs were prepared by firstsolubilizing specific amount of anhydrous iron (III) chloride powder(laboratory grade, Fisher Scientific Company, Toronto, ON, Canada) in 2mL deionized water to give final concentration of 2.5 M followed byaddition of a stoichiometric amount of NaOH_((s)) pellets (FisherScientific Company, Toronto, ON, Canada) under 200 rpm of mixing and 25°C. The color of the aqueous solution turned reddish brown signaling theformation of precipitate of Fe(OH)_(3(s)).

The particles were mixed with the invert emulsion drilling fluid in aslurry form. The fluids were mixed/highly sheared to achieve ahomogenous mixture using Hamilton beach mixer. FIG. 1 shows a schematicdrawing of the experimental procedure.

In situ preparation: This scheme of nanoparticle synthesis followed thetwo microemulsion method for nanoparticle synthesis (Husein and Nassar,2008). A 1 mL of 5 M FeCl_(3(aq)) was added to 250 mL of the drillingfluid, and in a separate vial 1 mL of 16 M NaOH_((aq)) was added to 250mL of the drilling fluid. The two vials were mixed overnight at 200 rpmand 25° C. Two control samples were prepared one containing theFeCl_(3(aq)) in the drilling fluid and another containing theNaOH_((aq)) in the drilling fluid and the samples were left to mixovernight at 200 rpm and 25° C. Finally to achieve a homogenous mixtureof the fluid samples and disperse the NPs more effectively, Hamiltonbeach mixer was used. FIG. 2 shows a schematic drawing of theexperimental procedure.

In another aspect, in situ NPs were prepared by adding the solidprecursors of FeCl₃ and NaOH at the stoichiometric ratio in smallbatches directly into the drilling fluid under high mixing and shearing.The water pools of the invert emulsion solubilize the solid precursors,and once solubilized, precursors react to form the solid product. Thesize of the Fe(OH)₃ product remains in the nano domain by virtue of thelimited size of the water pool, which, in turn, is preserved by thesurrounding layer of surfactant molecules. FIG. 3 is a schematicrepresentation of the process.

Calcium Carbonate Nanoparticles:

Calcium Carbonate NPs were prepared by aqueous reaction between Ca(NO₃)₂and Na₂CO₃ at specified temperature and rate of mixing as per thefollowing reaction (R2).

Ca(NO₃)_(2(aq))+Na₂CO_(3(aq))→CaCO_(3(s))+2 NaNO_(3(aq))   (R2)

Ex situ preparation: Calcium carbonate NPs were prepared by firstsolubilizing specific amount of anhydrous sodium carbonate powder in 5mL deionized water to give a final concentration of 2.26 M followed byaddition of 1 mL of 7.6 M stoichiometric amount of aqueous calciumnitrate under 200 rpm of mixing at 25° C. The color of the aqueoussolution turned white signaling the formation of precipitate ofCaCO_(3(s)) as per reaction (R2). FIG. 1 shows a schematic drawing ofthe experimental procedure. The product NP-slurry was mixed with thedrilling fluid under high mixing and shearing using Hamilton beachmixer.

In situ preparation: A 5 mL of 2.2 M sodium carbonate was added to 250mL of the drilling fluid and in a separate vial 1 mL of 7.6 M aqueouscalcium nitrate was added to 250 mL of the drilling fluid. The sampleswere left to mix overnight at 200 rpm and 25° C. Finally to achieve ahomogenous mixture of the fluid samples and disperse the NPs moreeffectively, Hamilton beach mixer was used. FIG. 2 shows a schematicdrawing of the experimental procedure.

3. LUBRICITY TESTING METHOD

A functional (drilling fluid lubricity) test was designed to simulatethe torque and drag produced by a given drilling fluid.

The lubricity test was designed to simulate the speed of rotation of thedrill pipe and the pressure the pipe bears against the wall of the borehole (OFITE lubricity test manual, 2011). It also predicts the wearrates of mechanical parts in known fluid systems. Lubricity property ofthe drilling fluid with NPs was evaluated by OFITE Lubricity Tester(Part no: 111-00, serial: 07-09, Houston, Tex.) at 150 inch-pounds oftorque which were applied to two hardened steel surfaces, a block andring rotating at 60 rpm rotational speed. The test sample was completelyimmersed between the ring and block. The apparatus ran for 5 min inorder to coat the metal test pieces with the sample fluid. The torqueadjustment handle was then turned until 150 inch-pounds of torque hadbeen applied to the test block. The machine again ran a 5 minstabilization period. A friction coefficient reading was then taken.Additional readings were taken every 5 min until three consecutivereadings agreed within ±2 units. The experiments involved threereplicates and the 95% confidence interval in Table 2 and Table 3 showhigh reproducibility of the test results.

The drilling fluid lubricity coefficient can be calculated using thefollowing equation as given in the Ofite manual (Ofite lubricity testermanual, 2011):

$\begin{matrix}{{{Coefficient}\mspace{14mu} {of}\mspace{14mu} {friction}} = {\frac{{lb}\mspace{14mu} {force}\mspace{14mu} {to}\mspace{14mu} {turn}\mspace{14mu} {the}\mspace{14mu} {ring}}{{lb}\mspace{14mu} {torque}\mspace{14mu} {load}\mspace{14mu} {applied}} = \frac{{Meter}\mspace{14mu} {Reading}}{100}}} & ({E1})\end{matrix}$

Coefficient of Friction (CoF) is used to quantify how readily twosurfaces slide in the presence of a lubricant or oil. It is a key factorwhich directly affects the torque and drag. The lower the value of thecoefficient of friction, the higher the lubricity or vice-versa.

The torque reduction, at a given load, can be calculated using thefollowing equation:

$\begin{matrix}{{{{Percent}\mspace{14mu} {torque}\mspace{14mu} {reduction}\mspace{14mu} {at}\mspace{14mu} {given}\mspace{14mu} {load}} = {\frac{( {A_{L} - B_{L}} )}{A_{1}} \times 100}}{{{Where}\mspace{14mu} A_{L}} = {{Torque}\mspace{14mu} {meter}\mspace{14mu} {reading}\mspace{14mu} {of}\mspace{14mu} {untreated}\mspace{14mu} {mud}\; ( {{inch}\text{-}{pounds}} )}}{B_{L} = {{Torque}\mspace{14mu} {meter}\mspace{14mu} {reading}\mspace{14mu} {of}\mspace{14mu} {treated}\mspace{14mu} {mud}\; ( {{inch}\text{-}{pounds}} )}}} & ({E2})\end{matrix}$

4. EFFECT OF NPS ON THE COEFFICIENT OF FRICTION

The engineered NPs in drilling fluid reduced coefficient of friction andsubstantially increased lubricity as shown in Table 2.

TABLE 2 Coefficient of friction and % torque reduction in the presenceand absence of NPs in drilling fluid (DF) Coefficient of friction DFwithout % torque reduction Nanoparticles (NPs) NPs DF with ex- DF within- DF with ex- DF with in- & Conc. Used (control) situ NPs situ NPssitu NPs situ NPs Fe(OH)₃ (1 wt %) 0.095 ± 0.002 0.081 ± 0.004 0.039 ±0.002 14.73% 58.94% CaCO₃(4 wt %) 0.095 ± 0.002 0.093 ± 0.002 0.059 ±0.006 2.1% 37.89%

It appears that in situ prepared NPs disperse better and communicatebetter with the mother drilling fluid as opposed to the ex situ preparedones. Therefore, in situ prepared NPs may carry a proportion of the loadbenefiting the improvement of antiwear property more than NPs preparedex situ. Thus using tailormade NPs in drilling fluid can reducecoefficient of friction and substantially increase lubricity.Improvement in lubricity reduces energy consumption, which, in turn,increases profitability.

Oil-based drilling fluids have the inherent advantage of significantlylower coefficients of friction (CoF). The typical CoF for an oil-baseddrilling fluid is 0.10 or less (metal to metal). In comparison, waterhas a CoF of 0.34 and the CoF of water-base drilling fluids typicallyranges between 0.2 and 0.5 (Chang et al., 2011). Comparing between thetypical oil based mud and NP-containing mud the friction mechanism ismost likely a transfer of NPs to the counterface. This suggests that NPsin the contact zone act like ball bearings in the interface between thetwo surfaces. The small size allows the particles to penetrate into thesurface and van der Waals forces ensure that the particles adhere to thesurfaces. Regular lubricants, or oil as continuous phase, in drillingfluid can only form a single oil film whereas NPs in drilling fluid cancreate an additional ball bearings action leading to better lubricationeffect.

Iron (III) hydroxide NPs perform better than calcium carbonate NPs. Afew iron oxide magnetite structures produced during the preparation ofiron oxide/hydroxide nanoparticles could possibly contribute to higherlubricity once captured in the surface within the drilling fluid. NaCland NaNO₃ salts form as side products during the iron oxide/hydroxideand calcium carbonate NP-based fluid formulation. According to someliterature (Scoggins and Ke, 2011; Ke and Foxenberg, 2010), sodium saltsimprove fluid lubricity. Table 3 shows that these side products, infact, increase the coefficient of friction. Therefore, the increase inlubricity observed when iron-based and calcium-based NP-drilling fluidsare used can be entirely attributed to the nanoparticles.

TABLE 3 Coefficient of friction and % torque reduction in the presenceand absence of salts in drilling fluid (DF) Salt & Conc. Coefficient offriction % torque Used DF without salt (control) DF with salt reductionNaCl (1 wt %) 0.0980 ± 0.002 0.100 ± 0.004  −2% NaNO₃(1 wt %) 0.0980 ±0.002 0.110 ± 0.005 −12%

Nanosized particles are much more readily dispersible than micron-sizedones (Canter, 2009). When dispersed in a drilling fluid, minimumagglomeration and settling occur and a stable suspension form. Thestable dispersion is also supported by the presence of surfactantmolecules. Both in situ and ex situ prepared nanoparticles are so smallin size that a stable colloidal dispersion in drilling fluids can beachieved which probably avoids the undesired precipitation caused bygravitation. With the formation of a stable well-proportioneddispersion, NPs are more prone to be trapped in the rubbing surface dueto its excessive surface energy. Dispersed nanoparticles are depositedon the friction surface and sheared off nanoparticles trapped at theinterface. Roughness of the surface may be reduced by the polishingeffect (Wu et al, 2007; Mosleh et al., 2009). Moreover, thenanoparticles tend to be dispersed uniformly which would result in amore uniform contact stress between the contacting surfaces (Chang andFriedrich, 2010). Moshkovith et al. (2007) studied the lubricityproperties of IF-WS₂ and also found dispersion impacts the lubricityperformance as the dispersed NPs possess solid lubrication propertiesdue to its stability. It was also found that aggregates size of NPsdepend on the mixing time of dispersion. The NPs are engineered to havespecific size ranges and shapes so that they can find their way intointricate spaces and maintain lamellar structure. It is thereforespeculated that the coefficient of friction reduction is due to thesurface boundary films provided by NPs that slide easily over oneanother like ball bearings. Similar findings have been reported in theliterature on the effect of dispersing carbon and metallic-based NPs ontribological performance of lubricating oils (Ajay et al., 2008;Abdullah, 2008; Verma et al., 2008; Zhang et al., 2009). Specifically, areduction in the coefficient of friction by over 25 percent was observedwhen adding nickel-based NPs to lubricants (Kostic, 2010).

In addition to reducing torque, higher lubricity also lowers theincidence of stuck pipe, which can significantly lower drillingefficiency. Estimation prepared by oil companies showed that stuck pipewhile drilling costs more than $250 million each year (Q'Max TechnicalBulletin #7). Minimizing friction and the ability to transfer the weightto the bit are very important factors in drilling highly deviatedextended reach and horizontal wells. Moreover, reduction in torque inthe presence of NPs signifies higher extended reach wells at a giventorque and load on bit.

From the aforementioned discussion it can be pointed out that theability of NPs to increase lubricity depends on the following features:

-   -   1. NPs can adsorb physically on any metal surface due to van der        Waals forces.    -   2. The size of the NPs is so small that they can easily enter a        macroscopic sliding contact.    -   3. The lubrication effect can be generated by the chemical        nature of the surfactant as described by Yang et al.(2012) and        NPs altogether or NPs alone. Dispersed nanoparticles help reduce        agglomeration at the interface and hence, improve the        co-efficient of friction. Surfactant can be used to improve the        dispersion quality and stability.    -   4. Coefficient of friction is significantly reduced by NPs alone        and salts produced as side products from the NPs formation have        no impact on lubricity.

The NP additives are multifunctional. NPs-based lubricants can be usedin automobile, lubricants, greases, metal working fluid, heavy machineryand other related industries. Standard laboratory tests indicated thatNPs lowered both API and HTHP drilling fluid loss values. It can, also,improve the rheological property and lifting capacity. It has strongadsorption ability and can adhere to the wall and the string and thusimprove lubricity. Addition of NPs enhances the load-bearing capacity ofthe lubricants, preserving the surfaces in direct contact and thereforeincreases the wear resistance.

6. REFERENCES

Abdullah. S. F, “Nanoparticle (capped wolfram (VI) Oxide) as a additivein lubricant”, ICCBT, 347-356, (2008)

Amanullah. M, Al-Arfaj. K. M, and Al-Abdullatif. Z, “Preliminary TestResults of Nano-based Drilling Fluids for Oil and Gas FieldApplication”, SPE/AIDC 139534, 1-9, (2011)

Canter. N, “Boron nanotechnology-based lubricant additive”, Tribologyand lubrication technology, (2009)

Chang. Li, Friedrich. K, “Enhancement effect of nanoparticles on thesliding wear of short fiber-reinforced polymer composites: A criticaldiscussion of wear mechanisms”, Tribology International, 43, 2355-2364,(2010)

Husein. M, Zakaria. M. F, Hareland. G, “Novel nanobased drilling fluidsto mitigate fluid loss” PCT Patent Application No: PCT/CA2012/050075,(2012)

Husein. M. M, Nassar. N. N, “Nanoparticles Preparation using the singlemicroemulsion scheme”, Current Nanoscience, 4, pp 370-380, (2008)

Hoskins. W. T, “Drilling fluid additive and method for improvinglubricity or increasing rate of penetration in a drilling operation”, USPatent Publication 2010/0204067 A1, (2010)

Javora. P. H, Qu. Q, “Well treatment fluids containing nanoparticles andmethods of using same”, US Patent Publication 2009/0082230 A1, (2009)

Ke. M and Foxenberg. W, “Lubricity of brine completion and workoverfluids”, SPE/ICoTA 130679, 1-7, (2010)

Kercheville. J. D, Hinds. A. A, Clements. W. R, “Comparison ofenvironmentally acceptable materials with diesel oil for drilling mudlubricity and spotting fluid formulations”, IADC/SPE 14797, (1986)

Kostic. M, “Development of hybrid, tribological nanofluids with enhancedlubrication and surface-wear properties”,www.kostic.niu.edu/DRnanofluids, (2010)

Krishna. R, Chandrakant R. P, Prabhakar S. P, Sairam KS. P., Craig R.,Ricky C, Jiter C and Chad D. B, “Lost circulation compositions andassociated method”, US Patent Publication 2011/162845 (2011)

Lammons. A. D, “Field Use Documents Glass-bead Performance”, Oil & GasJ. 82, No. 48, 109-111 (1984)

Malshe. P. A, Adhvaryu. A, Verma. A and McCluskey. H. P,“Nanoparticulate based lubricants”, US Patent Publication 2008/0234149A1 (2008)

Moshkovita. A, Perfiliev. V, Verdyan. A, Lapsker. I, Popovitz-Biro. R,Tenne. R and Rapoport. L, “Sedimentation of IF-WS₂ aggregates and areproducibility of the tribological data”, Tribological International,40, 117-124, (2007)

Mosleh. M, Atnafu D. N, Belk H. J, Nobles M. O, “Modification of sheetmetal forming fluids with dispersed nanoparticles for lubrication”,Wear, 267, 1220-1225, (2009)

Ofite Lubricity Tester Instruction Manual, OFI Testing Equipment Inc,(2011)

Q'Max Technical Bulletin #7, “Differentially Stuck Pipe”, Q'MaxSolutions Inc

Qi. Q and Paul H. J, “Well treatment fluids containing nanoparticles andmethod of using same”, US Patent Publication 2009/0082230 (2009)

Riley. M, Stamatakis. E, Young. S, Hoelsher P. K, Stefano D. G,“Wellborestability in unconventional shale-the design of a nanoparticles fluid”,SPE 153729, (2012)

Scoggins. C. W and Ke. M, “Method of increasing lubricity of brine-baseddrilling fluids and completion brines”, U.S. Pat. No. 8,071,510 (2011)

Skalle. P, Backe. R. K, Lyomov. K. S, Kilaas. L, Dyrli. D. A and Sveen.J, “Microbeads as Lubricant in Drilling Muds Using a ModifiedLubricity”, SPE 56562, 1-7, (1999)

Tenne. R, Rapoport. L, Lvovsky. M, Feldman. Y and Leshchinsky. V,“Hollow fullerene-like nanoparticles as solid lubricants in compositemetal matrices”, U.S. Pat. No. 6,710,020 (2004)

WU. Y Y, Tsui. Wc, Tc. Liu, “Experimental analysis of tribologicalproperties of lubricating oils with nanoparticles additive”, Wear, 262,819-825, (2007)

Yang. Z, Liu. Y, Zhao. X, Song. T, Yan. J, Jia. W, “Research andapplication of nanoscale emulsion lubricating material for drillingfluid in Daqing oil field”, IADC/SPE 161899, 1-7, (2012)

Zakaria. M. F, Husein. M, Hareland. G, “Novel Nanoparticle BasedDrilling Fluid with Improved Characteristics” presented at SPEInternational Conference on Oilfield Nanotechnology held in Noordwijk,The Netherlands on 12-14 Jun., 2012, SPE-156992-PP

Zhang. M, Wang. X, Fu. X and Xia. Y, “Performance and anti-wearmechanism of CaCO₃ nanoparticles as a green additive inpoly-alpha-olefin”, Tribology International, 42, 1029-1039, (2009)

The above-described aspects are intended to be examples only.Alterations, modifications and variations can be effected to theparticular example by those of skill in the art without departing fromthe scope, which is defined solely by the claims appended hereto.

1-34. (canceled)
 35. A method of making a well fluid, the methodcomprising steps of: forming an emulsion that includes an oil phase anda water phase; preparing a plurality of precursor materials separatelyfrom the emulsion, the precursor materials including hydrophilicreagents that are capable of reacting to form nanoparticles upon mixingof the precursor materials, adding the precursor materials to theemulsion; and thereafter mixing to distribute reagents from theplurality of water-based precursor solutions for in-situ reaction withinthe water phase, the nanoparticles formed by virtue of the in-situreaction being present in an amount of less than 5% by weight of thewell fluid but which are also effective amounts to improve lubricity ofthe well fluid.
 36. The method of claim 35, wherein the step of formingan emulsion includes forming the well fluid as a water-in-oil emulsionwhere oil is a continuous phase of the emulsion, and the step of addingthe plurality of water-based precursor solutions leaves oil as thecontinuous phase.
 37. The method of claim 36, wherein the step offorming an emulsion includes adding a primary emulsifier and a secondaryemulsifier to stabilize the emulsion.
 38. The method of claim 35,wherein the step of forming an emulsion includes adding a primaryemulsifier and a secondary emulsifier to stabilize the emulsion.
 39. Themethod of claim 35, wherein the step of preparing the plurality ofprecursor materials includes dissolving at least one of the reagents inwater prior to the step of adding the precursor materials.
 40. Themethod of claim 35, wherein the step of preparing the plurality ofprecursor materials includes dissolving all of the reagents in waterprior to the step of adding the precursor materials.
 41. The method ofclaim 35, wherein the step of preparing the plurality of precursormaterials includes preparing at least one of the reagents as a solidmaterial for direct addition to the well fluid during the step of addingthe precursor materials to the emulsion.
 42. The method of claim 35,wherein the step of preparing the plurality of precursor materialsincludes preparing all of the reagents as solid materials for directaddition to the well fluid during the step of adding the precursormaterials to the emulsion.
 43. The method of claim 35, further includinga step of introducing additional materials to formulate the well fluidas a type of drilling fluid.
 44. The method of claim 35, furtherincluding a step of introducing additional materials as needed toformulate the well fluid as a type of well kill fluid.
 45. The method ofclaim 35, further including a step of introducing additional materialsas needed to formulate the well fluid as a type of well completionfluid.
 46. The method of claim 35, further including a step ofintroducing additional materials as needed to formulate well fluid as atype of well pre-stimulation fluid.
 47. The method of claim 35, furtherincluding a step of introducing hydrophilic clay.
 48. The method ofclaim 35, wherein the water phase utilized in the step of forming theemulsion is a brine.
 49. The method of claim 48, wherein the brine is acalcium chloride brine.
 50. The method of claim 35, wherein the oilutilized in the step of forming the emulsion is a low aromatichydrotreated oil.
 51. The method of claim 35, wherein the nanoparticlesare formed as the reaction products of iron chloride and sodiumhydroxide.
 52. The method of claim 35, wherein the reagents react toform iron hydroxide nanoparticles.
 53. A well fluid made according tothe method of claim
 35. 54. A well fluid made according to the method ofclaim
 36. 55. A well fluid made according to the method of claim
 39. 56.A well fluid made according to the method of claim
 41. 57. A well fluidmade according to the method of claim 35, the well fluid beingformulated as a type of well fluid selected from the group consisting ofa well drilling fluid, a well kill fluid, a well pre-stimulation fluidand a well completion fluid.
 58. A well fluid made according to themethod of claim
 49. 59. A well fluid made according to the method ofclaim 52.